1. Field of the Invention
The present invention relates generally to welding of refractory materials with low expansion and loss coefficients. More specifically, the present invention applies to welding of fused quartz using a high power LASER (Light Amplification by Stimulated Emission of Radiation) as a heat source.
2. Description of Related Art
Laser welding or laser fusing is the process of uniting two formerly separate pieces of material by the application of heat via an intense energy beam along the area of contact between the pieces. The physical barriers originally associated with the separate pieces of material along the area of contact are changed, thereby allowing the pieces to join. One method of accomplishing this task is melting or softening the edges of materials and compressing them. In many cases a filler rod is used to place filler material in gaps between angled pieces of material to be joined. The filler rod melts when exposed to the heat source and joins with the contact areas of the pieces being welded. Generally this has the effect of reinforcing the weld, but occasionally the process will introduce impurities into the weld between the materials, thereby making the weld weaker.
Unfortunately, even in laser welding, one of the weakest spots in a weld is the weld joint. This weakness may be attributed to a variety of reasons. For example, the filler material may not successfully bond with the materials being joined; as is often true in the case of quartz. Furthermore, the thermal expansion of the material during the welding process often creates or introduces imperfections into the materials being joined. For example, materials with a high thermal expansion coefficient introduce solidification cracking as the weld cools. In addition, the laser welding process often introduces impurities into the materials that weaken the material. For example, laser-welding quartz generates silicon oxides, which contaminate the weld or are deposited on the quartz surfaces. What is needed is a method of generating a full penetration weld without introducing structural weakness.
In addition to properly welding materials that other heat sources can join, laser heat sources are also useful in welding materials that are difficult to join, such as high carbon stainless steels and titanium. In fact, lasers may even be used to weld dissimilar materials, which would otherwise be incompatible using other traditional welding techniques. Despite this usefulness with most difficult to weld materials, the refractory or amorphous materials still pose a substantial difficulty to presently available laser welding devices. Unfortunately, many of the refractory materials, such as quartz, are amorphous materials with no precise melting temperature. The weld joint must be carefully monitored to ensure that the weld is not too hot, thereby altering the material into a fluid state that drips away from the fillet. Examples of welding techniques and welding monitoring systems can be found in U.S. Pat. Nos. 4,443,684, 5,155,329, 5,534,103, 6,1,88,041, and 6,191,383.
Although lasers can cut refractory materials, such as quartz, lasers have difficulty welding refractory materials due in part to the amorphous nature of the materials. Despite the potential usefulness to the semiconductor industry, laser fusing of quartz and other refractory materials remains largely unexplored. This is due in part to the unreliability and difficulty of creating full penetration welds in the refractory materials. Refractory materials include quartz, sapphire, rutile, and other refractory materials with a low thermal expansion coefficient. Generally, a weld of these materials requires substantial heat, which affects a larger area then would normally be desired. Furthermore, oxides that are generated during the welding process may contaminate the surface of the weld before the weld can cool down and solidify. What is needed is a method of generating full penetration uncontaminated welds of refractory or amorphous materials, such as quartz, with no precise melting temperature.
The present invention has been developed in response to the current state of the art, and in particular, in response to these and other problems and needs that have not been fully or completely solved by currently available laser welding techniques and apparatus. Thus, it is an overall object of the present invention to provide full penetration laser welding via high power lasers characteristically selected for the material being welded. This can be accomplished by selecting a laser as a heat source that is adjusted so that the laser is absorbed by the material to be joined. An example of an apparatus facilitating quartz welding is shown in FIGS. 1 and 2.
The present invention facilitates full penetration welds of refractory materials, such as quartz, sapphire, rutile, and other materials with a low thermal expansion coefficient. These qualities are primarily accomplished through optimizing the radiation from a heat source so that it is almost completely absorbed by the materials to be welded. For example, fused quartz may be optimally welded by a high power carbon dioxide laser with a characteristic wavelength of 10.6 xcexcm in the mid-infrared portion of the electromagnetic spectrum. By selectively varying power, focus, and feed rates of the carbon dioxide laser, the laser emits radiation that is almost completely absorbed by the quartz material. Other lasing media can be selected based on the desired emission wavelength, power needed, and pulse duration.
Accordingly, one aspect of the apparatus is to facilitate full penetration welds.
Another aspect is that the apparatus maintains the integrity of the fused quartz material, keeping the welded materials free from cracking and contamination by oxides.
An additional aspect of the apparatus is that the heat-affected zone created during a quartz weld is kept to a minimum.
Yet another aspect of the apparatus is by varying laser type, focus, power, and feed rates full penetration welds may be created for other welded substances.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.